Posted
by
timothy
on Thursday October 16, 2008 @07:07PM
from the training-exercise-was-too-trite dept.

sash writes "From the fresh press release: 'Investigations at CERN following a large helium leak into sector 3-4 of the Large Hadron Collider tunnel have confirmed that cause of the incident was a faulty electrical connection between two of the accelerator's magnets. This resulted in mechanical damage and release of helium from the magnet cold mass into the tunnel.
Proper safety procedures were in force, the safety systems performed as expected, and no one was put at risk. Sufficient spare components are in hand to ensure that the LHC is able to restart in 2009, and measures to prevent a similar incident in the future are being put in place.'"

About 3.4 billion euros, and estimated to total around 6 billion euros in the end. Compared to a lot of other things, that isn't that much. Especially when you consider that several countries have been shouldering the cost together

Skimmed over the reference, page 6 states:"Some U.S. money has gone into the LHC, which will cost billions of dollars: five, maybe ten--the exact number is elusive (the science will be precise, but the accounting apparently follows the Uncertainty Principle)."

Contrast that with, say, the Joint Strike Fighter program+purchases:"Total development costs are estimated at more than US$40 billion (underwritten largely by the United States), while the purchase of an estimated 2,400 planes is expected to cost an additional US$200 billion.[49]"

If you really believed that, you'd never willingly board any aircraft.

Sure, things break down, whether electrical or mechanical. So what? That's why we conduct regular inspections, replace components based on established life-cycles, and conduct regular test-runs to ensure all systems function prior to being put into active service. Technicians aren't a bunch of witch-doctors, dancing around the machinery, shaking rattles, and moving components at random. It's a science like any other, and it produces repeatable results on which we can, and do, rely on to keep us safe and productive.

Actually, the quenches themselves are not the problem, these are quite under control and during the so-called training campaign something that is even deliberately induced.

The problem here is more a chain of unfortunate events, and something that wasn't expected during design.

Basically what happened is:- faulty electrical connection caused the power supply to trip (i.e. detect some problem and shut down)- fast discharge was triggered as a consequence- during fast discharge the current couldn't be handled by the faulty connection, causing an electrical arc- the arc burnt a hole into the insulation

This is the first thing that hadn't been considered in the design. The cold mass can withstand a very high helium pressure. Helium is not expected to go in the vacuum outside of the insulation (which is there as a thermal shield).

Then, the next problem:- the electric arc caused some bad electrical fluctuations, causing the quench protection system in several magnets to think there was a quench- as a consequence, the quench protection heaters then actually induced real quenches- as a consequence, a lot of Helium got evaporated, causing the Helium pressure in the cold mass to increase sharply

This wouldn't have been a real problem, hadn't there been the hole caused by the arc.

Now the Helium entered the thermal shield around the cold mass with high pressure, causing emergency shutters installed all 107 metersto close, which are there to protect the vacuum in the rest of the magnets. Unfortunately they were maximally designed to withstand a pressure of regular atmosphere and not the Helium under high pressure. As a consequence they were completely torn by the pressure, causing connections between magnets to be damaged and even more Helium to be released. Several hundreds of meters of tunnel were affected by this, which leads to my personal conclusion that the pressure must have broken several shutters in both directions, until they could finally hold.

So, as a consequence, the actual faulty electrical connection was a small problem compared to the chain reaction which caused in total 29 magnets to be damaged.

(Disclaimer: Personal interpretation of the incident report, there might be flaws in it)

I think it needs pointing out though that the LHC was always going to be shutdown over the next few months as a planned contigency period in-case of even bigger faults occuring then the one which did (or construction being delayed as was widely expected).

About a rounding error in the interest on the E2,000B the EU countries are spending bailing out their over-leveraged banks?

Contrary to the $700 billion bailout in the US, the EUR2000 billion figure in Europe is "just" guaranties to inter-bank credits. Ideally, this money is not spent at all (though some probably will). Eg in the case of Germany, the German government has set up a EUR500 billion program: EUR80 billion to provide fresh money to banks by temporarily buying stakes in them (if they want). EUR400 billion in guaranties for inter-bank credits. They (justified or not) think they take a 5% risk, meaning that they expect to spend about EUR20 billion for cases where they indeed have to pay for the guaranties.

The point is that the damage is worse that originally reported. Early reports indicated that the connections to a magnet had failed and the magnet had quenched, without damage to the magnet. That by itself wouldn't be too hard to fix, and probably could have been done in place. But, as it turns out, there was considerable damage to other magnets and vacuum lines. All this is in an underground tunnel, so access is tough. Especially since the LHC has less working room in the tunnel
than most other big accelerators.

The magnet assemblies are cylinders about 14m long, with both the superconducting coils and all the supporting vacuum and cryogenic plumbing. Now, several of those units have to be disconnected, moved carefully onto a transport car, moved very slowly to the big lift shaft, hauled up to the surface, repaired, returned to the tunnel, reconnected, and recommissioned.
Each one of those steps is a big, tough job.

Early papers claimed that a magnet quench would cause a few hours of downtime, not a few months.